Animal litters containing fuller's earth clays are well known in the art. More particularly fuller's earth clays comprised of the mineral montmorillonite and alumino silicates have been used in connection with animal litters, alone or in combination with other substances.
In most applications, the fuller's earth clay is calcined by heating it to a finishing temperature of more than 180.degree. C. to remove all of the free moisture and a portion or all of the interstitial moisture of the clay. Clay heated to a finishing temperature higher than 180.degree. C. but less than 1000.degree. C. is known as a lower volatile material ("LVM") clay. Such clay has no free moisture but some interstitial moisture. Fuller's earth clays which are calcined by heating them to a finishing temperature of more than 180.degree. C. are non-colloidal. Non-colloidal clays are those that do not form colloids when dispersed in a liquid environment such as water.
One disadvantage of the above described fuller's earth clays when used as an animal litter is that they do not form clumps when exposed to urine, or, if they do, such clumps are not cohesive. The clumps, for example, formed by LVM clay disintegrate completely when removed or dislodged. Another disadvantage is that they do not absorb the urine readily whereby the urine accumulates at the bottom of the litter box.
In order to improve the clumping and absorbing properties of fuller's earth clays, the clays are sometimes partially calcined to remove all of the free moisture thereof by heating them to a finishing temperature of not more than 180.degree. C., usually 120.degree. C. to 150.degree. C. Such clays are colloidal in that they form a colloid when exposed to or dispersed in a liquid environment such as an aqueous environment. These partially calcined clays are known as regular volatile material ("RVM") clays.
An animal litter being presently sold by Sanex Corporation of Houston, Texas, under the trademark Better Way.RTM. utilizes regular volatile material clay and, more particularly, regular volatile material attapulgite. Although such clay readily absorbs the urine and forms strong and cohesive clumps that can be removed, the clumps are occasionally broken by the animal when the animal burrows in the litter or by the animal owner when he removes the clumps from the litter box. The inventor has found that by increasing the free moisture content of the regular volatile material clay used as litter, the litter forms stronger and more cohesive clumps when exposed to urine. The addition of free moisture to a regular volatile material clay when used in connection with an animal litter has not been practiced in the past by anyone.
U.S. Pat. No. 4,437,429 discloses an improved animal litter that includes a non-colloidal fuller's earth clay and an effective amount of a hydrated zeolite. It is well understood by those skilled in the art that a non-colloidal clay is a clay that is calcined by being heated to a finishing temperature of more than 180.degree. C. One disadvantage of the animal litter disclosed in that patent is that the entire litter box must be disposed of after a certain period of time.
U.S. Pat. No. 4,085,704 discloses an animal litter that produces a continuous, long lasting, uniform, slowly released odor control agent. The patent discusses the addition of non-colloidal fuller's earth clay to the animal litter to reduce the cost of the litter.
U.S. Pat. No. 4,532,890 make reference to Japanese Patent Application Laid-Open No. 129622/1982 that discloses the use of zeolite as a deodorizer together with a bentonite. Bentonite is non-colloidal bentonite.
Although some of the animal litters utilizing fuller's earth clays form clumps when exposed to urine, the present invention discloses an animal litter that forms stronger clumps and a method of preparing such litter.
These and other objects and advantages of the present invention will become readily apparent from the following description.